This invention relates to an excavating tooth and, more particularly, to an excavating tooth having a unique connection between the point and adapter. As such, the invention relates to two-part teeth. At about the turn of the century, workers in the excavating art saw the merit of providing replaceable tips, viz., "points" on the tooth shank or adapter, so as to renew the penetrating portion without expensive down-time--see, for example, U.S. Pat. No. 564,664.
Over the years, many ways have been developed for mounting the point on the adapter--although, for the most part, these have taken the form of a wedge-shaped socket at the rear of the point which received a correspondingly shaped nose on the adapter. Almost at the outset of two-part teeth, it was seen to be possible to screw the adapter nose into a threaded socket in the point--see U.S. Pat. No. 784,116. However, notwithstanding the manifestly greater gripping power of a threaded connection, no commercial use of this has occurred during the last three-quarters of a century. In fact, the only teaching found of a threaded coupling for a point and adapter was in U.S. Pat. No. 2,145,663 issued in 1939. So for the past forty years no one has seen fit to utilize on the threaded connection.
It is surmised that one reason for this is the fact that the threads in the coupling really contributed nothing to the attachment--the principal securing means in U.S. Pat. No. 2,145,663 being a locking pin extending through the usual aligned openings in the point walls and adapter nose. A lock of some kind was essential to resist an unscrewing force. So notwithstanding the fact that a tightening force could be adequately resisted by the helical threads alone, these were ineffective when an unscrewing force was applied. This, in a practical sense the threads were superfluous.
It should be appreciated that the forces encountered by excavating teeth vary widely in direction location and magnitude. Because the consequences of a lost coupling are all out of proportion to the cost of the coupling--downtime of expensive equipment and repair in the primitive conditions of the field--locks and couplings have been engineered to stand up under the extraordinary and infrequently encountered force. Thus, a tooth that had a vulnerability to a force of one kind even though it possessed great strength to the opposite force, was manifestly unacceptable--except that a staunch lock be provided, and then the art was no better off than before.
According to the instant invention, a significant improvement has been made in the excavating tooth art by the combination of a helical thread coupling with a lock external to the coupling. An immediate advantage accuring from this arrangement is that the adapter nose can be solid, i.e., the heretofore commonplace locking pin opening is eliminated. It is in the area of the pin opening that most nose failures occur--so that art workers have had to "beef-up" this portion of the nose. Normally, the lock opening is positioned near the shoulder which joins the nose to the relatively massive adapter shank so that this has been an additional concern--providing an area of weakness immediately adjacent an area of transition, classically an area of incipient failure in itself. However, the wedge or tapered shape of the nose--dictated by the need for easy assembly and proper performance--also dictated that the pin opening be as rearward as possible so as to be in the section of greatest area, hence, strength. But, as pointed out just above, this intruded on the classically weak area of transition and aggravated the weakness.
However, by utilizing a solid threaded nose as the coupling means with the lock external thereto, the adapter is strengthened to such an extent that, according to preliminary tests, the rupture resistance of the nose in the inventive tooth is that of a conventional tooth one or two sizes larger, i.e., 20% stronger than the comparable prior art tooth of the same size. For example, teeth are generally sized according to the horizontal dimension across the rear of the point, expressed in inches--so the inventive tooth has the strength of a conventional tooth 1/2"-2" wider.
The provision of the external lock in combination with the threaded coupling provides a second and equally desirable advantage--the shear forces normally applied to the locking pin are converted to compressive forces so that a much smaller pin is used, again resulting in better use of the available metal in the tooth. It will be appreciated that in past teeth (whether of the type disassembled by unscrewing or just translation of the point) an impact tending to remove the point resulted in shearing forces at the ends of the locking pin. In other words, the movement of the inside of the point relative to the outside of the nose tended to shear the pin in the plane of movement. However, with the inventive arrangement, the movement of the point in a twisting fashion applies the nominally shearing forces at points where the locking pin is bolstered against a portion of the adapter--so that what ordinarily would be a shearing force is converted to a compressive force. Thus, the force that in conventional teeth would tend to transversely sever the metal now tends to elongate the same--against which the metal has much greater resistance.
Historically, locking pins have extended vertically through the point and adapter so as to facilitate disassembly. Horizontal pins have been used but have uniformly been considered "knuckle-busters" because of the difficulty of access. This impedes one principal function of the lock--to be easily removable so as to permit quick replacement of the point. The other principal function is, of course, to keep the point firmly mounted on the adapter against inadvertent removal.
The invention achieves the beneficial results of the vertical pin locks of the past by using rearwardly extending tongues on the point sides to provide the means adapted to receiving vertical pins--so that at the same time the lock is not only lateral and rearward of the threaded coupling section but also able to receive a vertical pin. Even further, the provision of the tongues reduces further the stress to be resisted--by at least 1/2--because two locks are available without sacrificing valuable wear metal.
Although rearwardly extending tongues on points have long been used--see U.S. Pat. No. 2,483,032--they have not been used so far as is known to the inventors hereof for locking, rather only for secondary stabilization. In fact, the only disclosure known to the inventors hereof using an external lock is U.S. Pat. No. 2,666,272. This, and co-owned U.S. Pat. No. 3,496,658, neither of which was employed commercially so far as known, are the only teachings where the aligned vertical lock openings were eliminated from the nose and point.
In the preferred form of the invention, an inverted U-shaped locking pin is employed which straddles the adapter and engages slots in the rearwardly extending tongues--thereby simultaneously achieving greater nose strength, the advantageous vertical removal while cooperating with the threads to avoid subjecting the pin to traditional transverse shearing in resisting unscrewing. Additionally the bight portion of the U-shaped pin is received within a transverse recess in the adapter top to protect the pin while providing means for such removal--and also while being located in the massive section of the adapter so as not to intrude into the areas of potential failure described above.
In the instance where a heavy impact load is concentrated near the tip of the tooth, it is advantageous to provide additional means for secondary stabilization generally following the principle of U.S. Pat. No. 3,079,710. The structures used previously to provide such stabilization viz., "flats" on the nose and socket have been made much more useful per se in the inventive tooth. The rotational movement for installing and removing the point on the nose according to the invention develops satisfactory confronting beam bearing surfaces even though they are helically developed curves. This has been greatly aided through extending the nearly square-sided thread means out to the tip of the nose of the adapter and apex of the point socket while positioning them at the corners of the nose and socket apices.
These terminal portions of the thread means have been found to be advantageous cooperating with the "flats" of the stabilized nose and socket to prevent "peeling" of the point from the adapter upon the application of concentrated impact loads by developing more stabilized bearing surfaces in the critical area.
In the preferred embodiment the ribs or thread means are nearly square-sided and non-uniform in cross-section along their length--being larger adjacent the nose or socket tips or apices as they are nearly circumscribable (less draft) inside a cylinder but are reduced in size toward the rear due to inscribed conical nose.
Other advantages, both general and specific, of the invention can be appreciated as this specification proceeds.